1. Industrial Application Field
The present invention relates to an interoffice multiparty connection method and an exchange implementing the interoffice multiparty connection method.
2. Prior Art
Advanced exchange service in the recent information network is required to be provided at different offices as well as at a local office. It is thus important to utilize all resources on the network for the effective and positive realization of the service. Multiparty connection service is an example of such service and is required to be provided among offices in a simple manner without deteriorating performance of an exchange.
The multiparty connection service is typically used to establish intercommunication (teleconference communication) among three or more parties. More specifically, when communication has been established between two terminals at the same office, an exchange of the office calls a third terminal at the same office in response to a request from either terminal to establish the intercommunication among these terminals. In other words, this multiparty connection service is provided by means of calling a terminal at an office in response to a request from either one of the terminals at the same office between which communication has been established and connecting lines for these three terminals to a multiparty connection trunk. In the multiparty connection service, a multiparty connection request may be made by designating two or more terminals at an office during calling from a terminal at the same office to establish intercommunication among the designated terminals and the calling party terminal.
The terminals to be serviced are not necessarily at one office. Instead, two or more terminals at a different office or offices may be subject to the multiparty connection service.
For example, it is assumed that communication has been established between a first terminal at a first office and a second terminal at a second office through a third office. When a user who uses the first terminal requires to establish multiparty connection among a third terminal at the second office, the second terminal, and the first terminal, this user transmits either hooking signal or a certain dialing signal (DTMF signal) from the first terminal to an exchange at the first office. This dialing signal (DTMF signal) includes a dialing signal indicative of a request for the multiparty connection service and a dialing signal indicative of a phone number of the third terminal. As a result of the transmission of the hooking signal or the DTMF signal, the exchange at the first office recognizes that the multiparty connection service is required. And the exchange at the first office acquires a conference trunk (multiparty connection trunk). Next, the exchange at the first office acquires a line between the first office and the third office. And the exchange at the first office supplies a connection control signal to the third office. This connection control signal designates to acquire a line between the third office and the second office.
In response to the connection control signal supplied from the first office, a exchange at the third office acquires a line between the third office and the second office, and supplies a connection control signal to the second office. This connection control signal designates to connect the acquired line to the third terminal.
A exchange at the second office calls the third terminal in response to the reception of the connection control signal supplied from the third office. The exchange at the second office connects the line acquired between the third office and the second office to the third terminal when the latter responds to the call.
Upon completion of the above mentioned process, the exchange at the first office connects the line connected with the first terminal to the conference trunk. And the exchange at the first office connects the line connected with the second terminal to the conference trunk. Further, the exchange at the first office connects a line connected with the third terminal to the conference trunk.
The conference trunk adds voice signals transmitted from the first terminal, the second terminal and the third terminal, and outputs the addition result to each terminal.
In the above mentioned conventional system, the multiparty connection trunk (conference trunk) at the first office is acquired and connected to the first terminal, the second terminal, and the third terminal. In this case, two lines between the first office and the second office are occupied until the communication (conference) is finished among the users between the first and third offices as well as between the third and second offices. Transmission lines for the transit can not be used effectively.
If all multiparty connection trunks at the first office are occupied, the first terminal cannot acquire any multiparty connection trunk. Accordingly, no multiparty connection is established in such a case. In order to overcome this problem, a multiparty connection trunk at a different office may be acquired by the first terminal. This method, however, requires the user at the first terminal complicated and bothersome operations. This is also true in an exchange on a network that supports an ISDN protocol when the multiparty connection is tried to be established over different offices.
Accordingly, an object of the present invention is to acquire a multiparty connection trunk automatically for the establishment of multiparty connection at an office where a communication line can be used effectively when a user while communication requests the multiparty connection over different offices on a network comprising of exchangers each of which supports an ISDN protocol.
Another object of the present invention is to acquire, when a multiparty connection trunk cannot be acquired at an office, the multiparty connection trunk at a different office. 1
Yet another object of the present invention is to attain above objects easily without affecting performance of the exchange.